Magnetic head gimbal assembly and magnetic disk unit

ABSTRACT

A magnetic disk unit includes a magnetic disk attached to a spindle so as to be rotatable, a slider having a magnetic head for reading/writing data onto/from the magnetic disk, a suspension for providing the slider with a predetermined load, and an actuator arm for positioning the slider attached to the suspension on the magnetic disk. A first pad including the magnetic head and second pads including no magnetic heads are disposed on an air bearing surface of the slider. During rotation of said magnetic disk, a part of the first pad keeps in contact with the magnetic disk. A load point of the suspension with respect to the slider is positioned between a leading edge of the slider and a position located at a distance equivalent to substantially 0.42 times a whole length of the slider from the leading edge of the slider.

[0001] This is a continuation of application Ser. No. 09/878,350 filedJun. 12, 2001, which is a continuation of application Ser. No.09/654,915 filed Sep. 5, 2000, which is a division of application Ser.No. 08/628,226, U.S. Pat. No. 6,157,519.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to magnetic disk units, and inparticular to a magnetic head slider and its suspension structure in amagnetic disk unit of contact recording type in which a magnetic headslider is brought into contact with a magnetic disk.

[0003] In order to increase the recoding density of magnetic disk units,the flying height between a slider for mounting a magnetic head and amagnetic disk had tended to be reduced. As the flying height is reduced,contact between the slider and the magnetic disk is becoming inevitable.Thus, there has been proposed a magnetic disk unit of the so-calledcontact recording type in which magnetic recording is performed with theslider brought into contact with the magnetic disk from the beginning.

[0004] In U.S. Pat. No. 5,041,932, there is disclosed an integralmagnetic head/suspension structure formed as a long and slender bentdielectric object or as a suspension having a magnetic head on one endthereof. This integral magnetic head/suspension has a feature ofextremely light mass. By reducing the mass of the integral magnetichead/suspension, the load applied to the magnetic disk can be reducedand wear between the magnetic head/slider and the magnetic disk can bereduced.

[0005] In a structure proposed in JP-A-6-251528, the flying forcegenerated by the air flow caused by rotating the magnetic disk under theintegral magnetic head/suspension assembly is canceled by mounting thesuspension section so as to form a suitable angle with respect to thesurface of the magnetic disk and thereby causing compressive force dueto air flow to act. In this structure, the contact state is maintainedover the entire surface of the magnetic disk.

[0006] In a positive pressure slider of flying/contact mixture typeproposed in JP-A-5-74090 and JP-A6-052645, a magnetic head is disposedon a center rail formed on a trailing edge of a positive pressure sliderof a flying type, and only the center rail having the magnetic head isbrought into contact with a magnetic disk to conduct magnetic recording.

[0007] In a negative pressure slider of the mixed flying/contact typeproposed in JP-A-62-167610, a trailing edge of a negative pressureslider of a flying type is brought into contact with a magnetic disk toconduct magnetic recording.

SUMMARY OF THE INVENTION

[0008] An object of the present invention is to reduce, in magnetic diskunits of the contact recording type, contact force between a slider anda magnetic disk so as not to damage the slider and the magnetic diskfatally.

[0009] Another object of the present invention is to provide a magneticdisk unit capable of maintaining uniform contact force over the entiresurface of a magnetic disk and conducting stable contact recording overa long period.

[0010] Another object of the present invention is to decrease frictionalforce caused in a contact portion between a slider and a magnetic diskwhen the slider is positioned on a data track on the magnetic disk by anactuator arm to such a degree as not to affect the positioning accuracy.

[0011] Still another object of the present invention is to restrictjumping of a slider from a magnetic disk caused by unsteady contactforce, debris on the magnetic disk, or vibration of the magnetic diskunit.

[0012] In accordance with a first aspect of an embodiment of the presentinvention, a first pad including a magnetic head and second pads whichdo not include a magnetic head are provided on an air bearing surface ofa slider of a magnetic disk unit. A part of the first pad keeps incontact with a magnetic disk when the magnetic disk is rotated, and aload point is positioned between a leading edge of the slider and aposition located at a distance of approximately 0.42 times the wholelength of the slider from the leading edge of the slider.

[0013] In accordance with a second aspect of an embodiment of thepresent invention, a trailing pad including a magnetic head and otherpads which do not include a magnetic head are provided on an air bearingsurface of a slider of a magnetic disk unit, and only the trailing padkeeps in contact with the magnetic disk while the magnetic disk is beingrotated whereas other pads are kept apart from and fly over the magneticdisk due to an air flow caused by the rotation of the magnetic disk, thecontact force between the trailing end pad and the magnetic disk beingat most 200 mgf.

[0014] In accordance with a third aspect of an embodiment of the presentinvention, a slider having a magnetic head includes, in its air bearingsurface, a first pair of positive pressure side pads located on theleading side, a second pair of positive pressure side pads locatednearly in the center in the slider length direction, and a positivepressure center pad located on the trailing edge side and containing themagnetic head, the area of the second positive pressure side pads beinggreater than the area of the first positive pressure side pads and thearea of the positive pressure center pad.

[0015] In accordance with a fourth aspect of an embodiment of thepresent invention, a first pad including the magnetic head and secondpads including no magnetic heads are disposed on the air bearing surfaceof the slider, and flying force generated by the first pad issufficiently smaller than flying force generated by the second pads. Themagnitude and pressure center of the flying force generated by thesecond pads is substantially coincident with the magnitude of the loaddriven to the slider by the suspension and the load point, and theslider is provided by a gimbal of the suspension with a moment force insuch a direction as to make the first pad approach the magnetic disk,only the first pad keeping in contact with the magnetic disk duringrotation of the magnetic disk.

BRIEF DESCRIPTION OF THE DRAWING

[0016]FIG. 1 is a side view showing the contact state between a sliderand a magnetic disk in an embodiment˜of the present invention.

[0017]FIG. 2 is an enlarged view of the slider and the magnetic diskshown in FIG. 1.

[0018]FIG. 3 is a top view showing the air bearing surface of the sliderillustrated in FIG. 1.

[0019]FIG. 4 is a graph showing the dependence of the normalized wearvalue upon the contact force applied between the slider and the magneticdisk.

[0020]FIG. 5 is a graph showing dependence of the contact force betweenthe slider and the magnetic disk upon the maximum roughness of themagnetic disk.

[0021]FIG. 6 is a graph showing the pressure distribution of the slider.

[0022]FIG. 7 is a graph showing dependence of the contact force betweenthe slider and the magnetic disk upon the sum of the mass of the sliderand the equivalent mass of a suspension.

[0023]FIG. 8 is a graph showing dependence of the flying height upon theradial disk position in a slider of the present invention andconventional sliders.

[0024]FIG. 9 is a graph showing dependence of the normalized contactforce upon the radial disk position in a slider of the present inventionand conventional sliders.

[0025]FIG. 10A is a side view showing the contact state between a sliderand a magnetic disk in another embodiment of the present invention.

[0026]FIG. 10B is a graph showing dependence of impulsive force Tapplied between the slider and a suspension illustrated in FIG. 10A upona distance x between a leading edge of the slider and a load point.

[0027]FIG. 10C is a side view showing the contact state between a sliderand a magnetic disk in another embodiment of the present invention.

[0028]FIG. 11 is a top view showing an example of an air bearing surfaceof a slider.

[0029]FIG. 12 is a top view showing another example of an air bearingsurface of a slider.

[0030]FIG. 13 is a side view showing the contact state between a sliderand a magnetic disk in another embodiment of the present invention.

[0031]FIG. 14 is a top view showing an air bearing surface of a slider.

[0032]FIG. 15 is a top view showing a magnetic disk unit with a rotaryactuator scheme using a slider of the present invention.

DETAILED DESCRIPTION

[0033] Hereafter, an embodiment of the present invention will bedescribed in detail by referring to drawing.

[0034]FIG. 1 is a side view illustrating the contact state between aslider and a magnetic disk in a magnetic disk unit of the mixedflying/contact type which is a first embodiment of the presentinvention. A predetermined load w is applied to a slider 1 by asuspension 2 via a load point A. A magnetic disk 3 is driven and rotatedby a spindle (not illustrated). As the magnetic disk 3 is rotated, anair flow is generated in a direction represented by an arrow V and itflows into a space formed between the slider 1 and the magnetic disk 3.This air which has flowed into the space between the slider 1 and themagnetic disk 3 is compressed between them, and the leading side of theslider 1 flies with flying force f2. The trailing edge of the slider 1comes in contact with the magnetic disk 3 while generating contact forcef1. Furthermore, frictional force f_(cr3) is generated in a contactportion B in a direction opposite to the air inflow direction as shownin FIG. 2. Denoting the distance measured from the load point A to thecontact portion B located between the slider 1 and the magnetic disk 3by L1 and denoting the distance measured from the load point A to apressure center C of the flying force f2 by L2, the slider 1 carries outcontact recording with respect to the magnetic disk 3 in such a postureas to satisfy the following two equations.

w=f1+f2  (1)

f1·L1=f2·L2  (2)

[0035] From these two equations, the contact force f1 is related to thethrust load w by the following equation. $\begin{matrix}{{f1} = \frac{{L2} \cdot w}{{L2} \cdot w}} & (3)\end{matrix}$

[0036] From equation (3), it will be appreciated that the substantialcontact force f1 can be made smaller than the load w in theslider/suspension of mixed flying/contact type by suitably selecting therelation between the distance L1 between the load point A and thecontact portion B and the distance L2 between the load action point Aand the pressure center C of flying force. On the other hand, in anintegral magnetic head/suspension having light mass and a light load,the load point and the contact portion are located nearly on a straightline. Since L1 is thus nearly 0 in this case, the load w becomes nearlyequal to the contact force fl. Although the contact force f1 can be madeless than the load w as expressed by equation (3) in theslider/suspension of mixed flying/contact type, the flying force betweenthe slider 1 and the magnetic disk 3 increases as the velocity of themagnetic disk 3 is increased, making it difficult to maintain the stablecontact state. Furthermore, according to the study of the presentinventors, the slider/suspension and the magnetic disk must satisfyvarious conditions for the magnetic head to maintain the stable contactstate over a long time without causing a fatal fault on the slider 1 andthe magnetic disk 3. These facts will now be described in detail byreferring to FIGS. 2 through 4.

[0037]FIG. 2 is an enlarged view of contact portions of the slider 1 andthe magnetic disk 3. The main body of the slider 1 is made of ceramicsuch as A1₂O₃TiC. On the air bearing surface, a slider overcoatincluding a silicon layer 11 and a carbon layer 12 is formed. Thesilicon layer 11 and the carbon layer 12 are 3 nm and 7 nm in thickness,respectively. As shown in FIG. 3, a magnetic head 13 is disposed on apositive pressure center pad 14 located at the trailing edge of theslider 1. On the other hand, a carbon overcoat 31 is formed on themagnetic disk 3 as well. For the purpose of preventing adhesion of theslider 1 and the magnetic disk 3, the magnetic disk 3 has a texture onit. A texture 32 of the magnetic disk 3 is formed by etching the carbonovercoat. As for the shape thereof, it is formed more uniformly than thetexture formed by widespread tape processing. As for the concretetexture shape, the top portion of the texture 32 takes the shape ofnearly a circle having a diameter of approximately 1 μm. The height d1of the texture 32 is approximately 15 nm, and the thickness d2 of thecarbon overcoat 31 left after etching. processing is approximately 10nm. The distance between texture w1 is approximately 10 μm. Therefore,the ratio of the area of the textures 32 to the area of the wholemagnetic disk is approximately 1%. Onto the carbon overcoat 31 of themagnetic disk, a lubricant is applied with a thickness of approximately2 to 4 nm.

[0038] In the case where the slider 1 conducts contact recording ontothis magnetic disk 3, the positive pressure center pad 14 of the slider1, contacts the top portion of the texture 32 and the distance betweenone texture and other texture is about, 10 μm which is very narrow ascompared with the length of the slider 1. Therefore, the slider 1 cannotperfectly follow the shape of the texture and comes in contact with thetop portion of the texture 32 as it slides. In the case where the slider1 and the magnetic disk 3 maintain the contact state, the contact areaof the slider 1 is overwhelmingly smaller than that of the magnetic disk3 and the carbon layer 12 serving as the overcoat of the slider 1 wearsearlier than the carbon overcoat 31 of the magnetic disk 3.

[0039]FIG. 3 shows an example of the air bearing surface of the slider 1used in the first embodiment. The slider 1 has, a length of 1.2 mm and awidth of 1.0 mm. The air bearing surface includes one pair of positivepressure side pads 15 and 16 located on the leading edge of the slider1, one pair of positive pressure side pads 17 and 18 located on nearlythe central portion of the slider 1 in the length direction, and apositive pressure center pad 14 having a magnetic head 13 and located onthe trailing edge of the slider 1. A width of the positive pressurecenter pad 14 is wide enough to mount the magnetic head 13 thereon. Thewidth is 200 μm, for example, in the present invention. The leading edgeof this slider 1 has no tapered surfaces and all positive pressure padshave substantially smooth planar surfaces. The magnetic gap of themagnetic head 13 is formed at a distance of approximately 40 μm from thetrailing edge of the slider 1. The magnetic gap is formed so as toprevent the magnetic head 13 from coming in direct contact with themagnetic disk 3 in reading/writing operation. Furthermore, the magnetichead 13 is a composite head having an MR head and a thin film head. TheMR head utilizes a magneto resistive effect and serves as a read head.The thin film head serves as a write-head. A recess 19 for isolatingrespective positive pressure pads has a depth of at least 50 μm and isadapted so as, not to generate a negative pressure therein. The load wapplied by the suspension 2 is 500 mgf. The load point A is set so as tocoincide with the center of the slider 1.

[0040] An experiment of contact reading/writing was conducted by usingthe slider 1 and the magnetic disk 3 for 1,000 hours continuously. FIG.4 shows dependence of the wear of the carbon layer 12 formed on thepositive pressure center pad 14 of the slider 1 upon the contact forcef1 in this case. The contact force f1 was measured by a piezo sensorwhich is mounted on the slider 1. The wear value was normalized by awear value obtained after contact had been performed for 1,000 hourscontinuously under the state that the contact force fl was kept at 500mgf equivalent to the load w. In order to change the contact force fl,the flying height of the slider 1 was changed diversely on a magneticdisk 3 having a texture height dl of 15 nm or the texture height dl ofthe magnetic disk 3 was changed diversely under the condition that theflying height of the slider 1 was constant. In the case where thecontact force fl of the slider 1 and the magnetic disk 3 was 100 mgf orless, wear of the carbon overcoat 12 of the slider 1 was extremelysmall. If the contact force fl became at least 100 mgf, the wear valueof the carbon overcoat 12 located at the trailing edge of the slider 1gradually increased. Until the contact force f1 reached approximately200 mgf, however, it could be observed that the carbon overcoat 12formed on the trailing edge of the slider 1 wore after continuouscontact state over 1,000 hours, but the wear debris did not stick to thepositive pressure pads 15 though 18 and the slider 1 could performflying/contact stably with respect to the magnetic disk 3 to the end.Reading and writing could be performed with no problem at all. At thistime, little wear could be observed on the top portion of the texture 32of the carbon overcoat of the magnetic disk 3 which is in contact withthe slider 1. This fact can be explained as follows. Immediately afterthe magnetic disk unit is started, the slider 1 is in contact with themagnetic disk 3 through a point or a line. As the wear of the carbonovercoat located on the trailing edge of the slider 1 advances, however,a newly generated surface of the carbon overcoat after wear becomes anew contact surface and consequently the contact pressure decreases.Until the contact force f1 reaches approximately 200 mgf, wear isconsidered not to advance if the area of contact is increased to somedegree. Furthermore, until the contact force f1 between the slider 1 andthe magnetic disk 3 reaches 200 mgf, the carbon overcoat is maintainedin the magnetic gap portion of the magnetic head 13 even aftercontinuous contact reading/writing operation lasting for 1,000 hours.The magnetic head 13 does not come in direct contact with the magneticdisk 3. The phenomenon that the output of the MR head is lowered due toheat generated by direct contact between the magnetic head 13 and themagnetic disk 3, i.e., the so-called thermal asperity is also prevented.

[0041]FIG. 5 shows dependence of the contact force f1 between the slider1 and the magnetic disk 3 upon the maximum surface roughness of themagnetic disk 3. If the texture height dl of the magnetic disk 3 isgreat and consequently the maximum surface roughness of the magneticdisk 3 is great or if debris formed by defective processing, forexample, is present on the magnetic disk 3, then the contact forcegenerated when the slider 1 comes in contact with that portion becomesextremely great and wear of the carbon overcoat of the slider 1 iscaused from that contact portion, resulting in an accelerated damage.The texture height dl of the magnetic disk 3 in the first embodiment isapproximately 15 nm. Since the magnetic disk 3 itself has undulation,however, the maximum surface roughness is approximately 20 nm. Forreducing the contact force f1 less than 200 mgf, the maximum surfaceroughness is desired to be 25 nm or less. This corresponds to thetexture height d1 of approximately 20 nm. On the other hand, if themaximum surface roughness of the magnetic disk 3 is in the mirrorlikestate, a large frictional force is generated in the contact portions ofthe slider 1 and the magnetic disk 3 and the contact force f1 abruptlybecomes large. Preferably, therefore, the maximum surface roughness isdesired to be at least 2 nm.

[0042] Furthermore, it is not necessary to form the carbon overcoat ofthe slider 1 on all of the positive pressure side pads 15 through 18 ofthe air bearing surface of the slider 1, but the carbon overcoat may beformed on the positive pressure center pad 14 of the trailing edge whichis in contact with the magnetic disk 3.

[0043]FIG. 6 is a graph showing the pressure distribution of the slider1. When seen from the length direction of the slider 1, the positivepressure pads 17 and 18 opposite to the load point A are the largest ascompared with the positive pressure pads 15 and 16 and the positivepressure center pad 14 as shown in FIG. 1. In addition, the slider 1 hasno tapered surfaces on the leading edge. Even in the case where thetrailing edge of the slider 1 keeps in contact with the magnetic disk 3as in the present invention, therefore, the pressure center C resultingfrom the air flow is formed near the load point A. The distance L2between the load point A and the pressure center C is thus shortened,and the contact force f1 can be reduced. In the present embodiment, thedistance L1 between the load point A and the contact portion B was 0.5mm and the distance L2 between the load point A and the pressure centerC was 0.1 mm. Furthermore, since the slider 1 has such pressuredistribution that the pressure becomes the maximum under the load point,the stiffness of the air bearing in the pitch rotational direction issmall. This is also effective in reducing the contact force fl.

[0044]FIG. 7 shows dependence of the contact force f1 upon the sum ofthe slider mass and suspension equivalent mass when the magnetic disk 3having a texture height dl of 15 nm and a maximum surface roughness of20 nm as described with reference to the first embodiment is used.Herein, the equivalent mass of the suspension 2 is a mass with which thesuspension 2 acts as effective inertia with respect to the movement ofthe slider 1 conducted in a direction perpendicular to the magnetic disksurface, and it is equivalent to a mass obtained when the suspension 2is approximated by a spring-mass model of a concentrated mass system.For making the contact force f1 equal to 200 mgf or less, it isnecessary to make the sum of the slider mass and the suspensionequivalent mass equal to 11 mg or less. In the first embodiment, the sumof equivalent masses of the combination of the slider 1 and thesuspension 2 was approximately 3 mg. For reducing the slider mass, it isnecessary to reduce the size of the slider. The size of the slider 1 isdesired to be at most approximately 2.0 mm in length and approximately1.0 mm in width. If the sum of the slider mass and the suspensionequivalent mass is too small, however, the load also becomes smallaccordingly and consequently handling becomes difficult in such a systemthat the slider 1 and the suspension 2 are separately formed as in thepresent invention. For facilitating handling, therefore, the sum of theslider mass and the suspension equivalent mass is preferably set equalto at least 2 mg.

[0045] As heretofore described, to reduce the contact force f1 reducingthe size of the slider 1 and increasing the distance L1 between the loadpoint A and the contact portion B are effective. However, they aremutually contradictory design parameters. Therefore, it is alsoimportant to reduce the load w to such a degree that the variance doesnot increase. Since the positive pressure pads of the slider 1 in thefirst embodiment has a substantially smooth surface and has no taperedsurfaces formed thereon, the load w can be minimized among the sliders 1having the same size. For making the contact force f1 equal to 200 mgfor less when the slider 1 in the first embodiment is used and reducingthe variance of the load w of the suspension 2, it is desired to set theload w equal to a value in the range of approximately 0.4 gf to 1.5 gf.

[0046]FIG. 8 shows the flying height profile, in the radial direction,of a magnetic disk having a diameter of 3.5 inch in the case where theslider 1 of the first embodiment, the conventional positive pressureslider and the conventional negative pressure slider are designed asflying type sliders. FIG. 9 shows the profile of the contact force. Thecontact force is represented as a value obtained by normalizing thecontact force in each radial position by the contact force of eachslider in an inner radius of the magnetic disk 3. The slider ofconventional mixed flying/contact type has the following problem. Whenthe position is located at an outer radius, i.e., as the peripheralvelocity is increased, the flying force increases and the stable contactstate cannot be maintained. In the slider according to the presentinvention, however, the flying height can be made nearly constant overthe entire surface of the magnetic disk as shown in FIG. 8. Therefore,the contact force can also be kept constant over the entire disk surfacewhile keeping the contact force at a sufficient small value with respectto the wear of the carbon. overc9at of the slider 1. The fact that thecontact force is kept at a nearly constant value over the entire disksurface means that stable contact reading/writing operation can beconducted over the entire disk surface. In the case of the conventionalpositive pressure slider, however, the velocity becomes greater andconsequently the flying height is increased when the position is locatedat an outer radius. As a result, the stable contact state cannot bemaintained in the case where the conventional positive pressure slideris used as the slider of a mixed flying/contact type.

[0047] Furthermore, in the case where the conventional negative pressureslider is used as the slider of a mixed flying/contact type, thenegative pressure increases as the position moves to an outer radius.Therefore, the flying height profile can be made nearly constant in thesame way as the slider according to the present invention. Since thenegative pressure becomes equivalent to the load w with respect to themagnetic disk, however, the contact force f1 becomes greater as theposition moves to an outer radius. Thus the risk of occurrence of afatal damage between the slider and the magnetic disk becomes greater.

[0048] Further features of a second embodiment will now be described byreferring to FIGS. 10A and 10B. In the magnetic disk unit of the contactrecording type as in the present invention, not only does a staticcontact force f1 steadily act on the contact portion B between theslider 1 and the magnetic disk 3 as described before with reference tothe first embodiment, but a dynamic impulsive force P which ishigh-frequency disturbance on the slider 1 from the magnetic disk 3 viathe contact portion B is also present. By this impulsive force P,impulsive force T acts on the suspension 2 from the slider 1 via theload point A. As a reaction thereof, the slider 1 receives the impulsiveforce T from the suspension 2. By the impulsive force T acting from thesuspension 2 on the slider 1 via the load point A, unsteady contactforce in the contact portion B between the slider 1 and the magneticdisk 3 increases. Or the slider 1 which has been in contact with themagnetic disk 3 is temporarily separated from the magnetic disk andthereafter hits the magnetic disk 3 again. This is called a jumpingphenomenon. This results in a problem that the magnetic disk 3 isdamaged fatally and reading/writing operation becomes impossible.

[0049] In reducing such trouble caused by a dynamic impulsive force, itis effective to dispose the load point A on a point which lies betweenthe leading edge of the slider 1 and the center of the slider lengthdirection as in the present embodiment. This effect will now bedescribed in detail by referring to FIG. 10B. FIG. 10B shows dependenceof the impulsive force T acting between the slider 1 and the suspension2 via the load point A when the impulsive force P has acted on thecontact portion B of the trailing edge of the slider 1, upon thedistance x between the leading edge of the slider 1 and the load pointA. When x=L, the load point A and the contact point B between the slider1 and the magnetic disk 3 are on the same axis of the slider thicknessdirection, and the impulsive force P acting between the slider 1 and themagnetic disk 3 becomes equal to the impulsive force T acting betweenthe slider 1 and the suspension 2. When x=0.5 L, i.e., when the loadpoint A is located on the center of the slider length direction and theload point A and the center of gravity of slider G are on the same axisof the slider thickness direction, the impulsive force P becomes equalto the impulsive force T. On the other hand, when 0.5 L<x<L, i.e., whenthe load point A is located on the trailing edge of the slider 1 withrespect to the center of the slider length direction, the impulsiveforce T which is greater than the impulsive force P acts between theslider 1 and the suspension 2. This increases the possibility that theslider 1 will hit the magnetic disk 3 with an impulsive force greaterthan the impulsive force P which has acted initially at the contactpoint B and the magnetic disk 3 will be damaged fatally. On thecontrary, when 0.5 L>x, i.e., when the load point A is located on theleading edge side of the slider 1 with respect to the center of theslider length direction, the impulsive force T acting between the slider1 and the suspension 2 becomes smaller than the impulsive force actingbetween the slider 1 and the magnetic disk 3 and consequently thepossibility of damaging the magnetic disk fatally is also decreased.Preferably, by letting 0.42 L>x, the magnitude of the impulsive force Tacting between the slider 1 and the suspension 2 can be made equal tohalf or less of the magnitude of the impulsive force P acting betweenthe slider 1 and the magnetic disk 3. In particular, when x=(⅓)L, therelation T=0 is satisfied and an impulsive force P which has actedbetween the slider 1 and the magnetic disk 3 on the contact portion B isnot transmitted to the suspension 2 via the load action point A, thusthere being no impulsive force from the suspension on the slider 1. Onthe contrary, even if any disturbance acts on the suspension 2, it isnot transmitted to the contact portion B between the slider 1 and themagnetic disk 3 via the load point A. By thus making the contact portionB and the load point A mutual centers of impact with the center ofgravity of slider G between, mechanical interaction in the verticalmovement direction is not present between the contact portion B and thesuspension 2 and mutual isolation of disturbance can be performed. Inaddition, by displacing the load point A to the leading edge side ofslider 1 with respect to the slider length direction, the distance L1between the load point A and the contact portion B becomes great asevident from equation (3) and the steady contact force fl can also bereduced simultaneously.

[0050] In reducing the jumping of the slider 1 from the magnetic disk 3caused by contact between the slider 1 and the magnetic disk 3 andreducing increase of unsteady contact force caused thereby, it iseffective to not only adopt the above described mechanical disturbanceisolating method but also to apply high polymer material such aspolyamide onto the suspension 2 as a vibration isolating material.Mounting a vibration isolating material on the suspension 2 has beenperformed in the case of the flying type as well. In a system such asthe contact recording type in which high-frequency distribution isexpected, however, the above described vibration isolating material ofthe suspension functions further effectively.

[0051] Furthermore, as another method for reducing the unsteady contactforce, it is effective to reduce the mass of the slider. For example,one method is to cut the recess portion located around the positivepressure center pad 14 as shown in FIG. 12 to reduce the mass of theslider 1.

[0052]FIG. 10C is a side view illustrating the contact state between theslider 1 and the magnetic disk 3 in a magnetic disk unit of the contactrecording type according to the second embodiment of the presentinvention. FIG. 11 shows an example of the air bearing surface of theslider 1 in the second embodiment. The slider 1 has a length of 1.2 mmand a width of 1.0 mm. The air bearing surface of slider 1 includes onepair of positive pressure pads 171 and 181 formed in positions oppositeto the load point A, and a positive pressure center pad 14 having amagnetic head 13 and located on the trailing edge. The depth of therecess 19 is at least 50 μm and a negative pressure is not generated.The load w given by the suspension 2 via the load point A is 500 mgf.This load w is nearly equal in magnitude to flying force f2 generated bythe positive pressure pads 171 and 181. Furthermore, the pressure centerC of the flying force f2 is made nearly the same as the load actionpoint A. In addition, flying force generated by the positive pressurecenter pad 14 of the slider 1 is negligibly small as compared with theflying force f2. In the present embodiment, the load point A is locatedon the leading edge side with respect to the center of the slider.Therefore, the distance L1 between the load point A and the positivepressure center pad 14 is sufficiently bigger than the distance betweenthe load point A and the pressure center G of the flying force f2generated by the positive pressure pads 171 and 181. Furthermore, thegreatest feature of the present embodiment is that moment Mp in such adirection as to thrust the positive pressure center pad 14 against themagnetic disk 3 acts on the slider 1 by not only applying the load wupon the load point A but also turning a gimbal 21 of the suspension 2by an angle θ in such a direction as to make the positive pressurecenter pad 14 approach the magnetic disk 3. In other words, a gimbalhaving much smaller stiffness than that of the loadbeam portion of thesuspension 2 is used to add the load f1 to the positive pressure centerpad 14. A very small contact load has thus been realized by using asimple configuration.

[0053] Equilibrium of force exerted between the slider/suspension andthe magnetic disk in the second embodiment can be expressed by thefollowing equations.

w

f2  (4)

[0054] $\begin{matrix}{{f1} = \frac{Mp}{L1}} & (5)\end{matrix}$

[0055] In the second embodiment, stiffness kp of the gimbal 21 in thepitch direction was set equal to 0.087 gf·mm/degree, and the distance L1between the load point A and the contact portion B of the positivepressure center pad 14 was set equal to 0.8 mm. In thisslider/suspension, the contact force fl can be set equal to 200 mgf, forexample, by tilting the pitch angle θ by 1.83° beforehand in such adirection as to make the positive pressure center pad 14 approach themagnetic disk 3. Processing of such a degree can be easily implemented.

[0056]FIG. 13 is a side view illustrating the contact state between theslider/suspension and the magnetic disk in a magnetic disk unit ofcontact recording type according to a third embodiment of the presentinvention. FIG. 14 shows an example of the slider in the thirdembodiment. In the slider/suspension of the third embodiment, the sliderflies in such state that the load w balances with the flying force f2generated by the positive pressure pads 171 and 181 in the same way asthe slider/suspension of the second embodiment. The positive pressurecenter pad 14 is subjected to a force equivalent to load f1 caused bythe moment of the gimbal 21 and it is in contact with the magnetic disk.In the third embodiment, a positive pressure rail 191 for generatingnegative pressure on the leading edge side of the positive pressurecenter pad 14 and a negative pressure recess 192 in which negativepressure is generated are formed as shown in FIG. 14 unlike the secondembodiment. The recess lg has a depth of at least 50 μm in the same wayas the first and second embodiments and generates only positivepressure. The negative pressure recess 192 has a depth of approximately6 μm. In the present embodiment, design is performed so that the flyingforce in this positive pressure rail 191 will be equal in magnitude tothe negative pressure generated in the negative pressure recess 192.Therefore, the flying force generated by this positive pressure rail 191and the negative pressure generated by the negative pressure recess 192do not affect the magnitude of the flying force and contact force of theentire slider. However, if the positive pressure rail 191 and thenegative pressure recess 192 are disposed on the air bearing surface ofthe slider 1 and air is effectively disposed between the slider and themagnetic disk, dumping of air is increased. Especially in the magneticdisk unit of contact recording type as in the present invention, thisair dumping effectively restricts vibration of the slider/suspension.

[0057]FIG. 15 is a top view of a magnetic disk unit with rotary actuatorscheme to which the above described configuration according to thepresent invention is applied. The slider 1 according to the presentinvention is subjected to seeking and positioning on whole data track ofthe magnetic disk 3 by a rotary actuator arm 4 via a suspension 2. Therotary actuator arm 4 is driven by a voice coil motor 5 in a directionrepresented by arrow D. With respect to magnetic head positioning, themost noticeable difference between the magnetic disk unit of the contactrecording type according to the present invention and the conventionalslider/suspension of flying type is that frictional force f_(cr2) actsbetween contact points of the slider and the magnetic disk in adirection opposite to the positioning movement direction at the time ofseeking and positioning. This frictional force f_(cr2) exerts greatinfluence upon the positioning precision of the magnetic head. If thefrictional force becomes great, then the magnetic-head gets out of thedata track in which the magnetic head should be positioned andreading/writing cannot be conducted. In the worst case, the actuatormight run away and the slider/suspension or the magnetic disk might bedestroyed. This frictional force f_(cr2) in the seeking and positioningdirection is defined by lateral stiffness k₂ of the suspension in theseeking and positioning direction and data track width T_(r) asrepresented by the following expression.

f _(cr2) ≦k ₂ ·T _(r)  (6)

[0058] Assuming that the track density is 20,000 TPI tracks/inch), thetrack width T_(r) is 1.27 μm. The lateral stiffness k₂ of the suspensionaccording to the present invention in the seeking and positioningdirection is approximately 0.24 kgf/mm, and the frictional force f_(cr2)in the seeking and positioning direction becomes approximately 300 mgf.For preventing the magnetic head from getting out of the data track inwhich the magnetic head should be positioned, therefore, it is at leastnecessary to make the frictional force f_(cr2) less than 300 mgf. If itis desired to increase the track density, it is necessary to increasethe lateral stiffness k₂ of the suspension 2 or reduce the frictionalforce f_(cr2) itself. Denoting the coefficient of friction between theslider 1 and the magnetic disk 3 by μ., load by w, and adsorptionbetween the slider 1 and the magnetic disk 3 by w_(s), the frictionalforce f_(cr2) can be represented by the following expression as well.

f _(cr2)≦(w+w _(s))  (7)

[0059] According to experiments conducted by the present inventors, thecoefficient of friction between the slider 1 of the present inventionand the magnetic disk having the texture height dl described withreference to the first embodiment was approximately 0.3. The load w ofthe suspension 2 is 500 mgf. For setting f_(cr2) equal to 300 mgf orless as described above, therefore, the adsorption w_(s) must be 500 mgfof less from expression (7). At the time of seeking and positioning, thepositive pressure center pad 14 is in contact with the magnetic disk 3and the area of that contact is approximately 0.02 mm2. Therefore,adsorption allowed per unit area of the contact portion B is 25 gf/mm².This is nearly equal to adsorption acting between the slider 1 and themagnetic disk 3 per unit area in the case where the magnetic diskdescribed with reference to the first embodiment having an textureheight d1 of 15 nm and an texture area ratio of 1% is used. Therefore,it is appreciated that the magnetic disk having the configurationdescribed with reference to the first embodiment is effective inreducing the frictional force f_(cr2) in the seeking direction as well.

[0060] Furthermore, when a slider/suspension of the contact recordingtype as in the present invention is recording on the same radius of amagnetic disk, or during seeking and positioning operation, frictionalforce f_(cr3) acts in the bit direction (circumference direction) of themagnetic disk. Unless this frictional force f_(cr3) in the bit directionalso satisfies a condition similar to that of the frictional forcef_(cr2) in the track direction (radius direction), precise positioningcannot be conducted. Denoting lateral stiffness in the bit direction,which is octagonal D to the seeking direction, of the suspension by k₃and bit width by T_(b), the following expression lust thus be satisfied.

f _(cr3) ≦k ₃ ·T _(b)  (8)

[0061] assuming now that the bit density is 500,000 BPI (bits/inch), thebit width becomes 0.05 μm. If the frictional force f_(cr3) in the bitdirection is desired to be nearly equal to frictional force f_(cr2) inthe seeking direction, the stiffness k₃ in the bit direction must be setequal to approximately 6 kgf/mm.

[0062] In the slider/suspension of the flying type, texture processingis conducted on the magnetic disk in order to reduce the frictionalforce at the time of starting. In the magnetic disk unit of contactrecording type, however, the texture of the magnetic disk is importantto reduce the frictional force not only at the time of starting but alsoat the time of seeking.

[0063] In the above described embodiment, texture processing isconducted on the magnetic disk side. Even if texture processing isconducted in the slider 1 side, however, a similar effect can beobtained. At this time, the magnetic disk 3 need not undergo textureprocessing, and the magnetic recording gap can be advantageously reducedby a value corresponding to the texture height d1.

[0064] As heretofore described, the contact force between the slider 1and the magnetic disk 3 can be made 200 mgf or less in the slider ofmixed flying/contact type according to the present invention. Inaddition, contact reading/writing operation can be conducted stably overthe entire surface for a longtime without depending upon the velocity.Furthermore, disturbances acting on the slider 1 from the magnetic disk3 and increasing of unsteady contact force. Furthermore, the contactforce at the time of seeking and positioning can be reduced, andaccurate positioning can be conducted even in contact recording.

What is claimed is:
 1. A magnetic disk unit comprising: a magnetic diskattached to a spindle so as to be rotatable; a slider which has a firstpad and second pads, and said first pad, which is keeping in contactwith said magnetic disk, has a magnetic head for reading/writing dataonto-from said magnetic disk and locates substantially in the center insaid slider width direction; a gimbal coupled to said suspension; asuspension which provides said slider with a predetermined load; and anactuator arm which positions said slider attached to said suspension onthe magnetic disk, said magnetic disk unit; wherein when denoting thecoefficient of friction between said slider and said magnetic disk by“μ”, load by “w”, and adsorption between said slider and said magneticdisk by “w_(s)”, and a frictional force of said friction by “f”, saidfrictional force “f” is equal or smaller than “μ(w+w_(s))”.
 2. Themagnetic disk unit according to claim 1, wherein said frictional force“f” is equal or smaller than 200 mgf.
 3. The magnetic disk unitaccording to claim 1, wherein said second pads are separated from saidmagnetic disk to fly by an air flow caused by rotation of said magneticdisk, and when said slider is seek-positioned on a certain track on saidmagnetic disk by said actuator arm via said suspension, said frictionalforce is equal or smaller than product of lateral stiffness of saidsuspension in a seek-positioning direction and a track width.
 4. Themagnetic disk unit according to claim 3, wherein a track density of saidmagnetic disk is equal or more larger than 20,000 TPI(tracks/inch). 5.The magnetic disk unit according to claim 3, wherein said frictionalforce is equal or smaller than 200 mgf.
 6. The magnetic disk unitaccording to claim 1, wherein when positioning is conducted contiguouslyon the same track on said magnetic disk while a contact state betweensaid first pad and said magnetic disk is being maintained, frictionalforce exerted between said first pad and said magnetic disk is smallerthan product of lateral stiffness of said suspension in a bit directionand a data bit width on said magnetic disk.
 7. The magnetic disk unitaccording to claim 6, wherein a bit density of said magnetic disk isequal or more larger than 500,000 BPI(bits/inch).
 8. The magnetic diskunit according to claim 6, wherein said frictional force is equal orsmaller than 200 mgf.